This invention relates to apparatus for controlling the operation of domestic appliances, such as clothes washers, dishwashers, dryers, and the like, and in particular to an electronic control apparatus which incorporates an electromechanical switching device.
Prior to the advent of solid-state electronic controls, most domestic appliances, such as automatic clothes washers, dishwashers, or dryers, used an electromechanical control device. An example of such a control device is shown in U.S. Pat. No. 2,703,347, issued to Constantine. This patent discloses a motor-driven control having a fixed array of switches sequentially actuated in a predetermined pattern by a cam disc incrementally rotating at a fixed rate to effect the cycling of the appliance through a predetermined sequence of operations over a predetermined period of time. The control was driven by a constant speed motor which acted as a timer to cycle the controlled appliance through desired operations over a period of time necessary, for example, to properly wash a load of dishes or clothing.
While the prior art Constantine device discussed above was highly reliable and relatively inexpensive, the capabilities of this device were severely limited. The cam disc was usually limited to 60 discrete angular positions for each full revolution of the cam disc, with each angular position being 6.degree. apart. The prior art Constantine device was thus limited in its ability to carry out multiple cycle operations or complex cycle operations.
An additional problem with these prior art electromechanical devices was the complexity involved in mechanically implementing the logic required to achieve the desired machine function. Complex programmed machine operations were often accomplished by multiple motor drives for a single or multiple cam and by the addition of one or more manually operated mechanical switches. This arrangement was very intricate mechanically, and was limited in the logic functions it could perform, due to the limited capabilities of the cam-activated mechanical switch.
To provide the capability demanded by modern appliances which have multiple cycles and complex cycle operations, solid-state electronic control devices have been adopted. Examples of such solid-state electronic control devices can be seen in the following U.S. Pat. Nos. 3,464,673, issued to Cargo et al.; 3,539,153, issued to Wennerberg et al.; 3,783,651, issued to Karklys; 3,922,889, issued to Karklys; 3,986,372, issued to Karklys; 4,001,599, issued to Karklys; 4,084,237, issued to Beachem et al.; 4,114,190, issued to Mazuir; 4,195,500, issued to Tobita et al.; and 4,222,250, issued to Torita.
These solid-state control devices have provided programming flexibility to accommodate complex cycle operations and a multiplicity of options in cycle operations. However, these solid-state control devices operated on low voltage, and to control the higher voltage elements of the appliance, such as motors, heaters, valves, and the like, it was necessary to employ various switching devices, such as relays, thyristors, SCR's, and the like. As a result, these solid-state electronic controls were often relatively expensive. In addition, the reliability of the control device was diminished by the plurality of discrete switching devices, such as relays or thyristors, each of which is subject to failure.